Lambdagt11 cDNA libraries derived from human brain poly A+ RNA were screened for recombinants that code for Alpha-subunits of G signal transduction proteins. Eleven alpha s and two alpha i clones were characterized. Four species of alpha s cDNA were found. A mechanism for generating the four species of alpha s mRNA by alternative splicing of precursor RNA was proposed. Treatment of NG108-15 neuroblastoma-glioma hybrid cells cAMP for several days results in the appearance of voltage-sensitive calcium channels and other ions channels. Twenty cDNA clones were obtained that hybridize to species of poly A+ RNA that increase in abundance 10-90 fold due to treatment of cells with dibutyryl cAMP. Affinity-purified antibodies to the Alpha or Gamma protein subunits of voltage-sensitive calcium channels were used to screen a Lambdagt11 cDNA library. Twenty putative voltage-sensitive calcium channel Alpha subunit cDNA clones and 29 putative Gamma subunit clones were found. Antigenic molecules termed TOP, which are distributed in a dorsal to ventral concentration gradient in chicken retina, were purified. TOP was shown to be a protein with an Mr of 47,000. The gradient of TOP in the retina is formed early in embryonic development. Thereafter, perpetuation of the gradient does not depend on the continuous presence of an extracellular gradient of diffusable molecules or on maintenance of interactions between cells. Synapses and neurites in the retina of developing chick embryos were reduced markedly by injection of anti-TOP antibody into the eye.